It is the purpose of this research proposal to study protein-protein interactions by using steady and nanosecond fluorescene methods. Two systems will be investigated, a) the interaction of retinol with several proteins involved in the specific binding of vitamin A. In addition to the mechanism of binding of all-trans retinol to RBP, we are going to study the association between the retinol binding protein (RBP) and prealbumin. The interaction of retinol with retinol dehydrogenase will also be investigated. In these studies we are using the fluorescence properties of a biological compound (retinol) which is transported by several proteins present in the blood. b) The interaction between concanavalin A and several glycoproteins. The results of this model studies are useful for the understanding of a more complex system, the reaction of an antigen with an antibody.